Automobile exhaust muffler



United States Patent [72] Inventor Francis W. Hamilton Southfield,Michigan [21] Appl.No. 851,228 [22] Filed Aug. 19, 1969 [45] PatentedDec.1,l970 [73] Assignee Chrysler Corporation Highland Park, Michigan acorporation of Delaware [54] AUTOMOBILE EXHAUST MUFFLER 3 Claims, 3Drawing Figs.

[52] U.S.Cl 181/59, 181/61 [51] lnt.Cl F01n l/02, FOln 1/08 [50] FieldotSearch 181/36, 36.2,48,54,59,64.1,61,62

[56] References Cited UNITED STATES PATENTS 2,035,923 3/1936 Scarritt181/64(.1)UX 2,075,265 3/1937 Bourne.... l8l/48X 2,106,482 1/1938Hargnett 181/48X 3,317,001 5/1967 Powers et a1 l81/48X PrimaryExaminer-Robert S. Ward, Jr. Attorney-Harness, Talburtt and BaldwinABSTRACT: An upstream exhaust pipe section is spaced axially from acoaxial tailpipe section of reduced diameter to provide an annular soundwave generating or driving gap for a reflective type tuning columndefined by an outer housing secured coaxially at its upstream anddownstream ends respectively to the upstream section adjacent the gapand to the tailpipe section. The latter is also supported coaxially atits upstream end adjacent the gap by a sliding interference fit withinward projections from the housing that accommodate relative thermalexpansion. Exhaust gases discharging axially across the annular gap fromthe upstream section into the tailpipe section generate in the tuningcolumn a muffling wave of length and amplitude determined respectivelyby the length and cross-sectional area of the tuning column, theamplitude of the muffling wave being enhanced by the impingement ofexhaust gases against the tuning column around the periphery of thereduced tailpipe section.

Patented Dec. 1, 1970 INVENTOR. fizz/(7s )4/ 54107172 02:

AUTOMOBILE EXHAUST MUFFLER BACKGROUND AND SUMMARY OF THE INVENTION Thisinvention relates to a muffler for the exhaustgases from an automobileengine and in particular to a rear or auxiliary muffler locateddownstream of the conventional primary muffler for the purpose ofattenuating comparatively low frequency sounds that pass through theprimary muffler. Coaxial straight-through mufflers of the generalconfiguration disclosed herein are well known to the art, as illustratedfor example in Cassel US. Pat. No. 3,348,629 and Hanchett U.S. Pat. No.3,323,613.

Such mufflers however are adaptations of the Helmholtz resonatorcomprising a tuning neck or throat acoustically connecting the exhaustgas passage and a resonator or tuning chamber so as to dampen soundvibrations in a frequency range determined substantially by the lengthand diameter of the tuning neck and the volume of the tuning chamber. Inorder to obtain the necessary volume for the tuning chamber and at thesame time minimize shell noise" characteristic of such mufflers,especially when the same are appreciably elongated it is necessary toincrease the overall diameter. With the increasing demand for a lowsilhouette vehicle body, the road clearance for such mufflers is notadequate for other than optimum smooth road conditions.

An object of the present invention is to provide an improved muffler ofthe above character wherein the customary resonator chamber is replacedby a reflective type tuning column that depends on its length ratherthan its volume for its muffling range, whereby the customary tuningneck is rendered unnecessary and a particularly efficient auxiliarymuffler of simplified and economical construction and reduced overalldiameter is achieved as compared to comparable mufflers availableheretofore.

Another object is to provide such a muffler that obtains the structuraladvantages of the above-mentioned Cassel type muffler, including theemployment of the exhaust passage as part of the muffler assembly,wherein the usual tailpipe section of the exhaust passage is spacedcoaxially from an adjacent discharge end of an upstream portion of theexhaust passage to provide an annular driving or sound wave generatinggap comprising the sole acoustical connection between the exhaust gasesand the aforesaid tuning column.

The latter comprises an outer shell secured coaxially around the exhaustpassage in sliding engagement with the tailpipe section adjacent anddownstream of the driving gap to support the tailpipe section in thedesired coaxial relationship. The tailpipe section is of slightlysmaller diameter than the aforesaid adjacent portion of the exhaustconduit upstream of the driving gap, such that the reflective tuner isdriven by direct impingement of the exhaust gases which materiallyincreases the efficiency of the muffler. Also by virtue of the shell ofthe tuning column supporting the tailpipe section, and the annulardriving gap spacing the tailpipe section from the adjacent upstreamexhaust pipe section, the maximum effective length for the tuning columnis obtained with a minimum overall muffler length with consequenteconomies and increased utility where length is a consideration, as forexample on some compact automobiles.

Other objects of this invention will appear in the following descriptionand appended claims, reference being had to the accompanying drawingsforming a part of this specification wherein like reference charactersdesignate corresponding parts in the several views.

FIG. 1 is a diagrammatic sketch of the automobile exhaust systemembodying the present invention.

FIG. 2 is an enlarged longitudinal section through the auxiliary mufflerillustrated in FIG. 1.

FIG. 3 is a transverse section taken in the direction of the arrowssubstantially along the lines 3-3 of FIG. 2.

It is to be understood that the invention is not limited in itsapplication to the details of construction and arrangement of partsillustrated in the accompanying drawings, since the invention is capableof other embodiments and of being practiced or carried out in variousways. Also it is to be understood that the phraseology or terminologyemployed herein is for the purpose of description and not of limitation.

BRIEF DESCRIPTION OF THE INVENTION Referring to the drawings, aparticular embodiment of the present invention is illustrated in FIG. 1showing an automobile engine 10 having the V-pipe 11 extending fromexhaust manifolds to a conventional muffler 12. The latter dischargesthrough an upstream exhaust pipe section 13, over a hump 14 for the rearaxle, and thence via a low frequency muffler 15 to an exhaust outlet 16.

FIG. 2 shows details of low frequency muffler 15 wherein the upstreamexhaust pipe section 13 terminates at an annular sound wave generatingor driving gap 17 and is welded at 18 immediately upstream of the gap 17to a reduced flange of a coaxial tubular shell or housing 19. Downstreamofthe gap 17, a smaller diameter tailpipe continuation 20 of the exhaustconduit extends coaxially through the housing 19 to the outlet 16. Thedownstream end of the housing 19 is provided with a reduced annularflange 21 welded to the tailpipe section 20 to complete a closedquarter-wave" tuning column 22 open only at the annular gap 17 into theexhaust gas flow. A plurality of staggered and circumferentially locateddimples 23 formed in the housing 19 snugly engage the upstream end ofthe tailpipe 20 at a sliding interference fit to accommodate thermalexpansion.

Ordinarily the conventional muffler 12 does not adequately muffle lowfrequency sounds so that the auxiliary low frequency muffler 15 isemployed. The frequency of the sound to be muffled depends solely on thelength of the tuning column 22 rather than on its volume as in thetypical Helmholtz resonator. Pressure variations within a lowerfrequency audible sound range and traveling with the exhaust gas flowgenerate a damping sound or pressure waves at the gap 17 that travel thelength of the tuning column and are reflected back to the gap 17substantially out of phase with the pressure waves in the exhaust gases,thereby to dampen the amplitude of such waves in accordance with wellestablished theory.

The sliding interference fit between the tailpipe section 20 and shell19 avoids mechanical vibration between these members and maintains thedesired coaxial alinement of the parts so that gases discharging fromthe periphery of the upstream exhaust pipe section 13 impinge againstthe upstream end of the column 22, thereby to increase the amplitude ofthe muffling wave generated at the gap 17 without necessitatingincreased cross-sectional area for the tuning column 22. In consequencea tuning column 22 of minimum cross-sectional area and outer diameter isachieved. Also the annular gap 17 opening radially into the axial column22 achieves an overall auxiliary muffler 15 of optimum efficiency andsimplicity with minimum axial and radial dimensions for a muffler of thetype shown.

The cross-sectional area of the annular column 22 is on the order ofmagnitude of the annular area across the gap 17 and is a function of theenergy or amplitude of the sound wave to be attenuated. An automobilemuffler suitable for damping sound vibrations in the low frequency rangeof approximately cycles per second or somewhat greater employs a wavegenerating gap 17 of approximately five-eighths of an inch in axiallength and a tuning column 22 approximately 30 inches long, which willbe approximately one-fourth or one-eighth of the wave length of theprimary sound waves to be attenuated.

The drawings are for illustrative purposes only and are not to scale.

The overall length of the column 22 could in some instances be slightlygreater than the length of a Helmholtz resonator of comparableeffectiveness but in the usual instance, the added length creates noproblem. On the other hand the reduced diameter achieved by the presentconstruction and the resulting increased road clearance are majoradvantages over conventional auxiliary muffler constructions.

lclaim:

' 1. In a reflective type exhaust muffler for an engine, conduit meansfor conducting exhaust gases from the engine and terminating in anupstream exhaust pipe section, a downstream tailpipe section extendingcoaxially from the terminal of said upstream section to receive exhaustgases therefrom, said tailpipe section having a forward end spaced fromthe terminal of said upstream section to provide an annular sound wavegenerating gap, an outer shell spaced coaxially from said tailpipesection a distance comparable to the length of said gap, said shelloverlapping said gap and extending rearwardly therefrom, closure meansconnecting the forward end of said shell to said upstream sectionadjacent and upstream of said gap and connecting the rearward end ofsaid shell to said tailpipe section to effect a reflective tuning columnclosed at its opposite ends and'opening at said gap directly into theflow of said exhaust gases for attenuating sound waves of lengthpredetermined substantially by the length and independently of thevolume of said tuning column, and cooperating means on said shell andtailpipe section for slidably supporting the forward end of the latterin coaxial spaced relationship with respect to said upstream section andshell to accommodate relative axial expansion and contraction of saidtailpipe section and shell.

2. In a muffler according to claim 1, said downstream tailpipe sectionhaving an external diameter slightly less than the internal diameter ofsaid upstream exhaust pipe section to effect direct impingement of gasesdischarging from said first pipe into the inner periphery of said tuningcolumn.

3. in the combination according to claim 1, said cooperating meanscomprising a plurality of spaced projections extending from at least oneof the members comprising said downstream tailpipe section and shell andslidably engaging the other of said members.

